1. Field of the Invention
The present invention relates to a thermostatic expansion valve, particularly to a thermostatic expansion valve which is suitable to be used, for example in an car air conditioner not only being needed to be small and light but also being subjected to vibration, centrifugal force, acceleration and deceleration, and more particularly to a thermostatic expansion valve which is suitable to be used in combination with an evaporator pressure regulator in the car air conditioner.
2. Description of the Related Art
The thermostatic expansion valve is used in a refrigeration cycle and FIG. 3 schematically shows a structure of a well-known refrigeration cycle. In the well-known refrigeration cycle, a compressor 10, a condenser 12, a reservoir 14, a thermostatic expansion valve 16 and an evaporator 18 are connected to one another in this order by a refrigerant pipe 20. The compressor 10 compresses refrigerant gas flowing into it and send the compressed refrigerant gas to the condenser 12. In the condenser 12, the compressed refrigerant gas is changed into refrigerant liquid because heat is taken off from the compressed refrigerant gas by air blown to the condenser 12 by a fan 22. The refrigerant liquid flown out from the condenser 12 is temporarily stored in the reservoir 14 and then flows into the thermostatic expansion valve 16, by which its pressure are rapidly lowered so that its temperature is also lowered. The refrigerant liquid pressure and temperature of which has been lowered takes heat off from air around the evaporator 18 so that it is gasified in the evaporator 18 and then flows into the compressor 10.
The thermostatic expansion valve 16 has a thermal bulb 16a for its valve member driving unit, and the thermal bulb is in contact with the refrigerant pipe 20 just after a refrigerant outlet of the evaporator 18. Further, an external pressure equalizing pipe 16b extending out from the driving unit to resist gas pressure supplied from the thermal bulb 16a is connected to the refrigerant pipe 20 at a downstream of the thermal bulb 16a.
The driving unit of the thermostatic expansion valve 16 drives a valve member by a pressure difference between a pressure of gas, generated in the thermal bulb 16a to corresponding to the temperature of refrigerant gas flowing just after the refrigerant outlet of the evaporator 18, and a pressure of the refrigerant gas introduced from the refrigerant pipe 20 through the external pressure equalizing pipe 16b. In this way, the thermostatic expansion valve 16 controls the amount of the refrigerant liquid which flows into the evaporator 18. More specifically, the thermostatic expansion valve 16 increases the amount of the refrigerant liquid flowing into the evaporator 18 when heat load in the evaporator 18 is increased so that the gasifying of the refrigerant liquid in the evaporator 18 is promoted and a difference of the temperature of the refrigerant gas flowing out from the refrigerant outlet of the evaporator 18 and an evaporation temperature of the refrigerant liquid in the evaporator 18 (that is, a degree of super heat) becomes large. In contrast thereto, the thermostatic expansion valve 16 decreases the amount of the refrigerant liquid flowing into the evaporator 18 when heat load in the evaporator 18 is decreased so that the gasifying of the refrigerant liquid is not promoted in the evaporator 18 and the temperature of the refrigerant gas flowing out from the refrigerant outlet of the evaporator 18 becomes substantially equal to the evaporation temperature of the refrigerant liquid in the evaporator 18. With such an operation, heat exchange efficiency in the evaporator 18 keeps at the highest level by controlling the amount of the refrigerant liquid flowing into the evaporator 18 on the basis of the magnitude of the heat load in the evaporator 18.
When the heat load applied to the evaporator 18 is small, moisture in the air is sometimes condensed and frosted on an outer surface of the evaporator 18. When the outer surface of the evaporator 18 is frosted, the heat exchange ability of the evaporator 18 is lowered. To prevent this, an evaporator pressure regulator 24 is attached to the refrigerant pipe 20 between the refrigerant outlet of the evaporator 18 and the refrigerant inlet of the compressor 10. The evaporator pressure regulator 24 serves to prevent an evaporation pressure of the refrigerant liquid in the evaporator 18 from becoming lower than a predetermined value so that the evaporation temperature thereof which corresponds to the evaporation pressure is prevented from becoming lower than a predetermined value and the above-mentioned frosting of moisture is prevented. The evaporator pressure regulator 24 is arranged in the refrigerant pipe 20 between the thermal bulb 16 and the pressure equalizing pipe 16b. With this arrangement, when the evaporator pressure regulator 24 closes the refrigerant pipe 20, the pressure difference between the pressure of the gas generated by the thermal bulb 16a which is positioned upstream of the evaporator pressure regulator 24, and the pressure of the refrigerant gas flowing from the external equalizing pipe 16b which is positioned downstream of the evaporator pressure regulator 24, is increased to make the thermostatic expansion valve 16 open. Therefore, the amount of the refrigerant liquid which flows into the evaporator 18 is increased, so that the temperature lowering of the evaporator 18 can be effectively prevented.
The above-described thermostatic expansion valve 16 having the thermal bulb 16a, however, is not suitable to be used in a car air conditioner because the independent thermal bulb 16a is connected to the thermostatic expansion valve 16 through a capillary tube. The thermal bulb 16a with the capillary tube makes the attachment of this thermostatic expansion valve 16 to a predetermined position in the car air conditioner in an assembly line thereof being difficult. In addition, the thermostatic expansion valve 16 is likely to be damaged because cars are susceptible at all times to vibration, centrifugal force, acceleration and deceleration.
In car air conditioners, a thermostatic expansion valve having such an arrangement as shown in FIG. 4 has been widely used. In a valve housing 30 of this thermostatic expansion valve, a first passage 32 and a second passage 34 are formed so as to be separated from each other in a vertical direction. The lower first passage 32 is arranged in a part of the refrigerant pipe 20 which extends from the reservoir 14 located downstream side of the refrigerant outlet of the condenser 12 to the refrigerant inlet of the evaporator 18 and the second passage 34 is arranged in a part of the refrigerant pipe 20 which extends from the refrigerant outlet of the evaporator 18 to the refrigerant inlet of the compressor 10.
A valve port 32a is formed in the first passage 32 to make the refrigerant liquid supplied from the refrigerant outlet of the reservoir 14 perform an adiabatic expansion. A center line of the valve port 32a extends a longitudinal direction of the valve housing 30. A valve seat is formed in an inlet of the valve port 32a, and a valve member 32b is urged toward the valve seat by urging means 32c such as a compression coil spring.
A valve member driving unit 36 is attached to a top of the valve housing 30. The unit 36 has a pressure-operating housing 36d an inner space of which is hermetically partitioned into upper and lower pressure-operating chambers 36b and 36c by a diaphragm 36a.
The lower pressure-operating chamber 36c of the pressure-operating housing 36d is communicated with the second passage 34 through a pressure equalizing opening 36e which is concentric with the center line of the valve hole 32a. A pressure of a refrigerant gas or vapor flowing from the refrigerant outlet of the evaporator 18 into the second passage 34 is applied to the lower pressure-operating chamber 36c through the equalizing opening 36e.
A valve member driving rod 36f is coaxially arranged in the equalizing opening 36e, and extends from a lower surface of the diaphragm 36a to the valve port 32a in the first passage 32. The valve member driving rod 36f is supported freely slidable in the vertical direction by an inner surface of the lower pressure-operating chamber 36c in the pressure-operating housing 36d and by a partition wall between the first and second passages 32, 34, and a lower end of the valve member driving rod 36f contacts the valve member 32b. A sealing member 36g is attached to a portion on an outer peripheral surface of the driving rod 36f, the portion corresponding to the partition wall between the first and second passages 32, 34, to prevent the refrigerant from leaking from the first passage 32 to the second passage 34 and vice versa.
Well-known diaphragm driving fluid is filled in the upper pressure-operating chamber 36b of the pressure-operating housing 36d. To the diaphragm driving fluid, the heat of the refrigerant vapor flowing from the refrigerant outlet of the evaporator 18 into the second passage 34 is transmitted through the diaphragm 36a and the valve member driving rod 36f exposed in the second passage 34 and the equalizing opening 36e communicated with the second passage 34.
The diaphragm driving fluid in the upper pressure-operating chamber 36b is gasified in response to the heat transmitted thereto and applies its pressure to an upper surface of the diaphragm 36a. The diaphragm 36a deflects in the vertical direction by a pressure difference between the pressure of the gas of the diaphragm driving fluid applied to the upper surface of the diaphragm 36a and a pressure applied to the lower surface of the diaphragm 36a. The pressure applied to the lower surface of the diaphragm 36a is a total of the pressure of the refrigerant vapor flowing from the refrigerant outlet of the evaporator 18 into the second passage 34, and an urging force of the urging means 32c applied to the valve member 32b in the first passage 32.
A displacement movement of the diaphragm 36a in the vertical direction is transmitted to the valve member 32b through the valve member driving rod 36f to make the valve member 32b approach or move away from the valve seat in the valve port 32a.
In this conventional thermal expansion valve, when the heat load in the evaporator 18 is increased and the degree of superheat (difference between a temperature of the refrigerant vapor and an evaporation temperature in the evaporator 18) of the refrigerant vapor flowing from the refrigerant outlet of the evaporator 18 into the second passage 34 is raised, the pressure difference increases in response to the rise of the degree of superheat so that the center portion of the diaphragm 36a is moved downward to move the valve member 32b away from the valve seat by the valve member driving rod 36f.
When the heat load in the evaporator 18 is decreased and the degree of superheat is lowered, the center portion of the diaphragm 36a is moved upward to allow the valve member 32b approach or sit on the valve seat by the urging force of the urging means 32c.
The conventional thermostatic expansion valve shown in FIG. 4, however, is not suitable to be used with the evaporator pressure regulator. The reason is as follows. If the evaporator pressure regulator is arranged in the refrigerant pipe 20 between the outlet of the second passage 34 of the thermostatic expansion valve and the refrigerant inlet of the compressor 10 as shown in the conventional example of FIG. 3, the pressure and temperature of the refrigerant vapor in the evaporator 18 can be prevented from lowering when the evaporation pressure of the refrigerant in the evaporator 18 is lowered to a predetermined value and the evaporator pressure regulator 24 is closed. Therefore, the pressure of the refrigerant vapor in the lower pressure-operating chamber 36c which corresponds to the pressure of the refrigerant vapor in the evaporator 18, and the pressure of the diaphragm driving gas in the upper pressure-operating chamber 36b which corresponds also to the temperature of the refrigerant vapor in the evaporator 18 are prevented at the same time from lowering, so that the difference of these both pressures is kept unchanged. The distance of the valve member 32b relative to the valve seat in the valve port 32a, therefore, is not changed greatly from that at the time when the evaporator pressure regulator starts its operation. This means that the amount of the refrigerant liquid flowing into the refrigerant inlet of the evaporator 18 through the valve port 32a is not changed greatly from that at the time when the evaporator pressure regulator starts its operation. Therefore, the temperature of the evaporator 18 cannot be rapidly prevented from lowering, and the frosting on the outer surface of the evaporator 18 cannot be effectively prevented.
A thermostatic expansion valve which is compact like as that shown in FIG. 4 of this application and can be used with the evaporator pressure regulator, is disclosed in FIG. 2 of U.S. Pat. No. 4,065,939 issued to Thornbery et al. In the thermostatic expansion valve, a valve member driving rod which extends from a diaphragm in a pressure-operating housing of a valve member driving unit on a top end of a valve housing to a valve member in a first lower passage and crosses a second upper passage, is hollow. This hollow portion in the valve member driving rod is closed at a bottom end thereof but opened at a top end thereof to communicate with an upper pressure-operating chamber in the pressure-operating housing.
Further, in the thermostatic expansion valve in FIG. 2 of the above described U.S. patent of Thornbery et al., a lower pressure-operating chamber in the pressure-operating housing is communicated with a refrigerant pipe through a pressure equalizing opening in downstream of an evaporator pressure regulator connected to an outlet of the second passage. In addition, a valve member driving rod penetrating opening which is formed in a partition wall between the lower pressure-operating chamber and the second passage is sealed by a combination of urging means and a sealing member both of which are arranged in the lower pressure-operating chamber.